1. Field of the Invention
The present invention relates generally to a method of manufacturing a semiconductor silicon single crystal wafer (hereinafter also referred to simply as a "silicon wafer" or a "wafer"), and more particularly, to a method of manufacturing a high quality epitaxial wafer which is required to improve electrical characteristics of the silicon wafer for use in manufacturing highly integrated semiconductor devices.
2. Description of the Related Art
Conventionally, silicon single crystal wafers made from a silicon single crystal, for use in highly integrated and miniatuarized semiconductor devices, have been produced by a Czochralski method (hereinafter the "CZ method") which is advantageous in manufacturing wafers of larger diameters.
Since the method of producing a silicon single crystal according to the CZ method utilizes a quartz crucible, oxygen atoms dissolved into a silicon melt from the quartz crucible are trapped into a silicon single crystal while the crystal is grown.
Such oxygen atoms exist at interstitial positions in a silicon single crystal in a super saturation state, so that they are deposited to form bulk micro defects (BMD) during heat treatment steps in fabricating semiconductor devices. Since the semiconductor devices have electrical circuits formed in the vicinity of a surface of the silicon single crystal wafer, BMD formed in such a region, if any, would cause problems such as a significant degradation of electrical characteristics such as time zero dielectric breakdown (TZDB) or the like.
To solve such problems, an intrinsic gettering (IG) heat treatment is generally used before a semiconductor device fabricating step as a particular pre-heat treatment.
This is a heat treatment method which involves a high temperature heat treatment conducted to a silicon wafer containing interstitial oxygen atoms, manufactured by the CZ method, to reduce the interstitial oxygen concentration on the surface of the silicon wafer through out-diffusion of the oxygen atoms therein, thereby forming a defect-free layer in the vicinity of the surface, and then heat treatment for oxygen precipitation nuclei formation at a low temperature to form BMD within the wafer.
With this treatment, the surface of the wafer, which serves as a semiconductor device fabricating region, is defect free, and the BMD incorporated within the wafer serves as gettering sites for heavy metal impurities during heat treatment steps or the like, thereby providing a high quality wafer.
However, in the recent increasingly highly integrated semiconductor devices, there are BMD remaining on the surface of the silicon wafer after the IG heat treatment due to an insufficient reduction of interstitial oxygen concentration, and a grown-in defect (see Semicond. Sci. Technol. 7, 1992, 135) introduced into a single crystal during crystal growth, which remains in the silicon single crystal wafer (see Jpn. J. Appl. Phys. Vol. 36, 1997 L591-594), thereby causing a problem of deteriorating electrical characteristics of the devices.
To solve these problems, in one method, a high quality semiconductor silicon single crystal wafer is produced by epitaxially growing a silicon single crystal on a silicon single crystal wafer. The epitaxial growth essentially differs from growth of a single crystal by the CZ method in the mechanism of growth. For example, when SiH.sub.2 Cl.sub.2 is used as a source gas, SiCl.sub.2 molecules dissolved at high temperatures chemically adsorb to hollow bridge sites.
Then, as Cl.sub.2 molecules are removed from the SiCl.sub.2 molecules through a surface reaction with H.sub.2 molecules, Si epitaxially and regularly grows on the silicon single crystal wafer in a parallel state. Therefore, according to this method, there can be produced silicon single crystal wafers which are for fabricating high quality semiconductor devices and free from micro-defects such as grown-in defects, without introducing growth striations in CZ crystal growth.
However, when a high interstitial oxygen concentration exists in a silicon single crystal wafer for epitaxial growth, interstitial oxygen atoms in the silicon single crystal diffuse into an epitaxial layer due to a heat treatment during epitaxial growth to form defects (see Extended Abstracts of The 42nd Spring Meeting, 28p-ZW-8, 1995, The Japan Society of Applied Physics and Related Societies), sometimes resulting in deteriorated electrical characteristics of semiconductor devices fabricated using such a silicon single crystal wafer.
While a manufacturing method has been proposed as measures taken against the above-mentioned problem by performing a high temperature heat treatment before epitaxial growth to reduce the interstitial oxygen concentration of a silicon single crystal wafer, this proposed method introduces another problem of industrially increasing a cost due to the addition of the heat treatment step.